Despite a great deal of progress in the delineation of factors involved in producing congenital defects in offspring form diabetics, congenital malformations remain the leading cause of fetal wastage among this group. Clinical approaches to the management of diabetics, which promote attempts to strictly regulate blood glucose concentrations, have reduced the incidence of malformations, but not eliminated them, and in fact have introduced a new threat to the offspring by causing maternal hypoglycemia. The spectrum of congenital abnormalities includes heart, neural tube and limb defects that are primarily thought to originate early (3rd-7th weeks) in gestation. Studies completed during previous years of support for this project using mouse embryos in culture have shown that the ketone body beta-hydroxybutyrate (BOHB) and hyperglycemia have a low teratogenic potential during gastrulation and neurulation. However, in combination there is an increase in the teratogenic effects. Mechanisms responsible for BOHB induced teratogenesis include altered DNA synthesis via a decreased de novo synthesis of nucleotides, whereas hyperglycemia may act by altering visceral yolk sac (VYS) function. Low molecular weight somatomedin inhibitors (LMWI) are potent teratogens and act by inhibiting DNA synthesis and altering VYS function through an undetermined mechanism. Finally, hypoglycemia, even for short exposure periods, is also a potent disrupter of embryogenesis during neurulation and may act by inhibiting glucose utilization. In future years, this project will continue to delineate factors contributing to the diabetic embryopathy and their mechanisms of action. Thus, the mechanism of hypoglycemia-induced teratogenesis will be defined by determining the effects of hypoglycemia on PPP and glycolytic metabolism, ATP production, and VYS function. Additionally, the sensitivity of gastrulation and early limb bud stage embryos to hypoglycemia will be assessed. The mechanism of altered VYS function produced by LMWI's will be determined and the teratogenicity of high molecular weight somatomedin inhibitors will be investigated in embryo and limb cultures. Other potential contributors to diabetes-induced malformations including antibasement membrane antibodies and the branched chain amino acids will be assessed for their potential to disrupt morphogenesis. Results from these studies will identify and define mechanisms of action of key factors in the origin or diabetes-induced embryopathies and will aid the clinician in counseling and managing the pregnant diabetic to produce a better outcome of pregnancy.